temp2d book 9-10
TRANSCRIPT
7/29/2019 Temp2d Book 9-10
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7.19. Summary ........................................................................................................................ 185
7.20. References...................................................................................................................... 187
8. STARTING AND SPEED CONTROL METHODS .............................................................. 189
8.1. Starting of cage-rotor induction motors ........................................................................... 189
8.1.1. Direct starting......................................................................................................... 189 8.1.2. Autotransformer starting ........................................................................................ 192
8.1.3. Wye-delta starting.................................................................................................. 193
8.1.4. Softstarting............................................................................................................. 194
8.2. Starting of wound-rotor induction motors........................................................................ 197
8.3. Speed control methods for cage-rotor induction motors .................................................. 199
8.3.1. The voltage reduction method................................................................................ 199
8.3.2. The pole-changing method..................................................................................... 201
8.4. Variable frequency methods............................................................................................. 202
8.4.1. V/f scalar control character istics............................................................................ 202
8.4.2. Rotor flux vector control........................................................................................ 206
8.5. Speed control methods for wound rotor IMs ................................................................... 210
8.5.1. Additional voltage to the rotor (the doubly-fed machine)...................................... 210
8.6. Summary .......................................................................................................................... 215
8.7. References........................................................................................................................ 216
9. SKIN AND ON LOAD SATURATION EFFECTS.............................................................. 219
9.1. Introduction...................................................................................................................... 219
9.2. The skin effect.................................................................................................................. 221
9.2.1. Single conductor in rectangular slot....................................................................... 221
9.2.2. Multiple conductors in rectangular slots: series connection .................................. 222
9.2.3. Multiple conductors in slot: parallel connection .................................................... 225 9.2.4. The skin effect in the end turns .............................................................................. 228
9.3. Skin effects by the multilayer approach ........................................................................... 230
9.4. Skin effect in the end rings via the multilayer approach.................................................. 236
9.5. The double cage behaves like a deep bar cage................................................................. 237
9.6. Leakage flux path saturation-a simplified approach ........................................................ 239
9.7. Leakage saturation and skin effects-a comprehensive analytical approach ..................... 242
9.7.1. The skewing mmf................................................................................................... 247
9.7.2. Flux in the cross section marked by AB (Figure 9.25) .......................................... 250
9.7.3. The stator tooth top saturates first.......................................................................... 250
9.7.4. Unsaturated rotor tooth top .................................................................................... 251
9.7.5. Saturated rotor tooth tip ......................................................................................... 252 9.7.6. The case of closed rotor slots ................................................................................. 253
9.7.7. The algorithm......................................................................................................... 253
9.8. The FEM approach........................................................................................................... 255
9.9. Standardized line-start induction motors.......................................................................... 260
9.10. Summary ........................................................................................................................ 261
9.11. References...................................................................................................................... 262
10. AIRGAP FIELD SPACE HARMONICS, PARASITIC TORQUES,
RADIAL FORCES, AND NOISE .......................................................................................... 265
10.1. Stator mmf produced airgap flux harmonics.................................................................. 265
10.2. Airgap field of a squirrel cage winding.......................................................................... 266
10.3. Airgap conductance harmonics ...................................................................................... 267
10.4. Leakage saturation influence on airgap conductance..................................................... 268
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10.5. Main flux saturation influence on airgap conductance .................................................. 270
10.6. The harmonics-rich airgap flux density ......................................................................... 270
10.7. The eccentricity influence on airgap magnetic conductance.......................................... 270
10.8. Interactions of mmf (or step) harmonics and airgap magnetic
conductance harmonics .................................................................................................. 272
10.9. Parasitic torques ............................................................................................................. 273 10.9.1. When do asynchronous parasitic torques occur? ............................................... 274
10.9.2. Synchronous parasitic torques............................................................................ 277
10.9.3. Leakage saturation influence on synchronous torques....................................... 280
10.9.4. The secondary armature reaction........................................................................ 282
10.9.5. Notable differences between theoretical and experimental
torque/speed curves ............................................................................................ 283
10.9.6. A case study: Ns/Nr = 36/28, 2p1 = 4, y/ = 1 and 7/9; m = 3 [7] ....................... 285
10.9.7. Evaluation of parasitic torques by tests (after [1]) ............................................. 285
10.10. Radial forces and electromagnetic noise ...................................................................... 286
10.10.1. Constant airgap (no slotting, no eccentricity)................................................... 288 10.10.2. Influence of stator/rotor slot openings, airgap deflection,
and saturation.................................................................................................... 288
10.10.3. Influence of rotor eccentricity on noise............................................................ 289
10.10.4. Parallel stator windings .................................................................................... 289
10.10.5. Slip-ring induction motors................................................................................ 290
10.10.6. Mechanical resonance stator frequencies ......................................................... 291
10.11. Summary ...................................................................................................................... 292
10.12. References.................................................................................................................... 294
11. LOSSES IN INDUCTION MACHINES................................................................................ 297
11.1. Loss classifications......................................................................................................... 297 11.2. Fundamental electromagnetic losses .............................................................................. 298
11.3. No-load space harmonics (stray no-load) losses in nonskewed IMs.............................. 300
11.3.1. No-load surface core losses ................................................................................ 300
11.3.2. No-load tooth flux pulsation losses .................................................................... 304
11.3.3. No-load tooth flux pulsation cage losses............................................................ 307
11.4. Load space harmonics (stray load) losses in nonskewed IMs........................................ 309
11.5. Flux pulsation (stray) losses in skewed insulated bars................................................... 313
11.6. Interbar current losses in uninsulated skewed rotor cages ............................................. 313
11.7. No-load rotor skewed uninsulated cage losses............................................................... 319
11.8. Load rotor skewed uninsulated cage losses.................................................................... 319 11.9. Rules to reduce full load stray (space harmonics) losses ............................................... 321
11.10. High frequency time harmonics losses......................................................................... 322
11.10.1. Conductor losses............................................................................................... 322
11.10.2. Core losses........................................................................................................ 324
11.10.3. Total time harmonics losses ............................................................................. 325
11.11. Computation of time harmonics conductor losses........................................................ 326
11.12. Time harmonics interbar rotor current losses............................................................... 328
11.13. Computation of time harmonic core losses .................................................................. 330
11.13.1. Slot wall core losses ......................................................................................... 330
11.13.2. Zig-zag rotor surface losses.............................................................................. 331
11.14. Loss computation by FEM........................................................................................... 332
11.15. Summary ...................................................................................................................... 335
11.16. References.................................................................................................................... 336